In a VTR of a type integrated with a camera such as a digital video camera or the like, it is typically practiced that audio sounds are gathered using a plurality of built-in microphones which are disposed at an arbitrary distance therebetween, and they are recorded as a stereophonic sound signal of two channels of L (left channel) and R (right channel) in a recording medium via a directivity calculation circuit.
Further, in an outdoor image shooting using the VTR of a type integrated with a camera, in most cases of conventional imaging, a wind noise due to a wind sound is inevitably collected together with an audio signal, which makes it very disturbing and irritating to listen thereto. However, a system for reducing such a disturbing wind noise has been provided in Japanese Patent Application Publications H11-69480 and 2001-186585, in which wind noise reduction circuits are proposed. In the wind noise reduction circuits, only wind noise signals are automatically reduced by use of circuits from a mixture of an audio signal and a wind sound signal gathered via microphones.
However, because their wind noise reducing circuits according to these methods disclosed in the Japanese Patent Application Publications H11-69480 and 2001-186585 are configured on the premise that the audio signals thereof are to be recorded as a stereophonic audio signals of 2 channels of L and R, they cannot deal with a recording of audio signals having 3 or more channels.
In other words, even in the case where three or more microphone capsules (microphone) are used, its wind noise reducing processing is carried out always after producing audio signals of two channels via a directivity calculation circuit such as for a stereophonic sound field processing or the like. Therefore, according to conventional wind noise reducing circuits, inmost cases, there has been a restriction that such a wind noise reducing circuit must be inserted in the subsequent stage of the above-mentioned directivity calculation circuit such as a circuit for the stereophonic sound field processing or the like, thereby preventing to achieve an advantage that can be enjoyed by inserting the wind noise reducing circuit in the preceding stage of the directivity calculation circuit in order to improve the performance and the freedom of system design.
Further, because the recording formats of the currently available digital videos can process up to 4 channels of multichannel recording, and because a camera-integrated VTR employing a multichannel recording such as a recent MPEG/AAC (Advanced Audio Coding), Dolby digital, DTS (Digital Theater System) systems is expected to be introduced, the provision of an automatic wind noise reducing circuit capable of dealing with the multichannel recording of the audio signals is desirable.
In consideration of the above, an object of the present invention is to provide an automatic wind noise reducing circuit and a method therefor, which are capable of solving the above-mentioned problems, dealing with multi-channeled audio signals, and improving its performance and freedom of system design.